The present invention relates generally to antennas, and more particularly to antennas used with wireless communications devices. Radiotelephones generally refer to communications terminals which provide a wireless communications link to one or more other communications terminals. Radiotelephones may be used in a variety of different applications, including cellular telephone, land-mobile (e.g., police and fire departments), and satellite communications systems. Radiotelephones typically include an antenna for transmitting and/or receiving wireless communications signals. Historically, monopole and dipole antennas have been employed in various radiotelephone applications, due to their simplicity, wideband response, broad radiation pattern, and low cost.
However, radiotelephones and other wireless communications devices are undergoing miniaturization. Indeed, many contemporary radiotelephones are less than 11 centimeters in length. As a result, there is increasing interest in small antennas that can be utilized as internally-mounted antennas for radiotelephones.
It is also becoming desirable for radiotelephones to be able to operate within multiple frequency bands in order to utilize more than one communications system. For example, GSM (Global System for Mobile) is a digital mobile telephone system that operates from 880 MHz to 960 MHz. DCS (Digital Communications System) is a digital mobile telephone system that operates from 1710 MHz to 1880 MHz. The frequency bands allocated for cellular AMPS (Advanced Mobile Phone Service) and D-AMPS (Digital Advanced Mobile Phone Service) in North America are 824-894 MHz and 1850-1990 MHz, respectively. Since there are two different frequency bands for these systems, radiotelephone service subscribers who travel over service areas employing different frequency bands may need two separate antennas.
There is also a growing trend towards development of radiotelephones which perform multiple functions. For instance, radiotelephones may incorporate Global Positioning System (GPS) technology or Bluetooth(trademark) wireless technology. GPS is a constellation of spaced-apart satellites that orbit the Earth and make it possible for people with ground receivers to pinpoint their geographic location. Bluetooth technology provides a universal radio interface in the 2.45 GHz frequency band that enables portable electronic devices to connect and communicate wirelessly via short-range ad hoc networks. Radiotelephones incorporating these technologies may require additional antennas tuned for the particular frequencies of GPS and Bluetooth.
Thus, as noted in U.S. patent application Ser. No. 09/193,587, entitled Portable Radiotelephones Including Patch Antennas, to William O. Camp, Jr., assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference, radiotelephones including GPS receivers have typically used an additional antenna to provide GPS reception. For example, quadrafilar helix antennas extending from the radiotelephone body have been used. The size constraints on these antennas, however, may reduce the gain available using quadrafilar helix antennas. Moreover, these antennas may be oriented at less than ideal angles and/or may be too close to the user""s body when used during telephone communications further reducing gain. Accordingly, there continues to exist a need in the art for improved antennas for GPS receivers incorporated into radiotelephones.
Recently, the Federal Communications Commission (FCC) has promulgated rules requiring that all cell phones be able to transmit their location during a 911 emergency call. As a result, when a user makes an emergency (911) call, the cell phone can be used to precisely determine the user""s location and transmit that location as a part of the emergency (911) call. The FCC approach is defined as Enhanced 911 (E911)Call Completion. The FCC requirements for E911 are described in FCC Document No. 94-102 (available at www.fcc.gov/e911/). One way the FCC requirements for E911 may be satisfied is by providing a cell phone with a separate GPS antenna.
In the few cases that a GPS function has been included in a cell phone product, the GPS antenna has typically been a patch antenna. For example, see U.S. patent application Ser. No. 09/193,587, entitled Portable Radiotelephones Including Patch Antennas, to William O. Camp, Jr., wherein a large GPS patch antenna is located on the front face of a cell phone. Although this configuration may enhance isolation, it may also undesirably disable the GPS function when the cell phone is in a normal talk position. Moreover, large patch antennas may be undesirable in today""s shrinking cell phones. In addition, externally mounted GPS antennas may be aesthetically undesirable.
A GPS antenna and a primary antenna within a wireless communicator, such as a cell phone, may be in close proximity. Interference and/or coupling between the two antennas may degrade the performance of both antennas. For example, a circuit coupled to one antenna may absorb power coupled to it from the other antenna thereby reducing efficiency of the other antenna. Alternately, a circuit coupled to one antenna may reflect power coupled from the other antenna thereby distorting a radiation pattern for the adjacent antenna.
As such, there is a need for GPS antennas that are small in size, that are inexpensive to manufacture, and that can be isolated from other antennas within a wireless communicator, such as a cell phone.
Notch antennas are well known antenna structures. Notch antennas have a radiation pattern which allows for uniform reception in all directions except for one or more relatively small angular regions where there is a null having a relatively steep slope. Notch antennas may be formed by etching a single side of a unitary metallically clad dielectric sheet or electrodeposited film using conventional photoresist-etching techniques.
FIG. 3A shows a perspective view of a conventional hand-held two way radio shown partially cut away to illustrate the location of a notch antenna. FIG. 3B illustrates a more detailed perspective view of the conventional notch antenna of FIG. 3A. In particular, U.S. Pat. No. 4,723,305 to Phillips et al. discloses an improved antenna configuration for a fully duplex portable radiotelephone that is normally operated in the nearly horizontal position next to the user""s ear and mouth. A notch antenna is provided in the bottom portion of the portable radio transceiver parallel to the major longitudinal axis of the housing. Phillips et al. suggest that the notch 80 aperture is cut in the conductive radio housing 78 at a transverse angle to the major face plane of the radiotelephone to form a notch antenna which radiates predominantly vertically polarized E-field waves when the transceiver is positioned such that the major longitudinal axis of the radio is approximately horizontal. U.S. Pat. No. 4,723,305 also discloses that the notch 80 is positioned in the bottom portion 20 of conductive housing 78 such that a plane passing through the notch is perpendicular to the major surface plane of the housing (which is parallel to the X-Y plane). Significantly, the notch 80 is cut in the bottom of the case such that the antenna is located under an operator""s hand. The other ends of coaxial cables 86, 88 are attached to radio circuitry 90 as shown.
In view of the above discussion, notch antennas that can be internally incorporated into wireless communicators and that are functional in a variety of orientations are provided. As used throughout, a xe2x80x9cwireless communicatorxe2x80x9d may refer to analog and digital radiotelephones, multiple mode radiotelephones, high function Personal Communication Systems (PCS) devices that may include large displays, scanners, full size keyboards and the like, and laptop, palmtop and pervasive computing devices that include wireless communications capabilities.
According to first embodiments of the present invention, an antenna for an electronic device includes a printed circuit board (PCB). The PCB has RF circuitry thereon that receives or transmits RF signals. The PCB also has a surface and an elongated configuration that defines a first direction. The PCB includes a ground plane conductor. A notch antenna is formed in the ground plane conductor. The notch is preferably not cut into the dielectric material of the PCB. Integrating the antenna function into the same PCB on which the transmitter and/or receiver functions are also located eliminates the need for an additional antenna component, and as a result may reduce manufacturing costs. It should also be appreciated that by using a notch antenna, the resultant gain coverage volume may be relatively large in comparison to other antenna structures (e.g., a patch antenna). The portion of the PCB underlying the notch is void of conductors, associated with other circuit functions, on all layers of the PCB. For instance, in one embodiment, the notch is simply a narrow rectangular area in which all conductors on all layers of the board have been cleared. This cleared area is free of line traces and components, especially large components such as a speaker and a liquid crystal display. In addition, shielding cans are preferably designed to avoid covering the notch area.
The notch may be formed in the ground plane conductor along a second direction transverse to the first direction. Preferably, the second direction is horizontal when the PCB is oriented such that the first direction is vertical. The notch can be defined by opposite side portions, a closed end, and an open end. For example, the notch could be configured to have opposite side portions that (1) are substantially parallel, (2) have a meandering configuration, (3) have a mirror image configuration, or (4) that have a flared open configuration. A closed end of the notch may have a width greater than the width of the open end of the notch to increase the effective length of the notch.
The notch antenna also includes an RF signal feed electrically connected to each of the side portions of the notch and to the RF circuitry that receives or transmits RF signals. The RF signal feed can be any unbalanced line that is connected to one side portion of the notch and that extends across the notch to the ground plane conductor on the opposite side portion of the notch. For example, the notch may be fed from a microstrip line on one side of the notch connecting across the notch to the ground plane on the opposite side of the notch. Under certain notch configurations the notch may be naturally resonant, and a feed point can be found along the length of the notch that matches the impedance to 50 Ohms (or some other desired impedance) without any additional components. On the other hand, if the notch is not resonant it can be matched to a desired impedance by either dielectrically loading the PCB or by using at least one impedance matching circuit. While the impedance matching circuit could theoretically have many possible configurations, the impedance matching circuit may include at least one of a series capacitor that bridges the notch adjacent the open end and/or at least one shunt capacitor positioned adjacent a side portion of the notch. When RF signals are applied to the side portions via the RF signal feed, and the PCB is oriented such that the first direction is vertical, the notch preferably has a configuration that results in predominantly vertically polarized electromagnetic waves being radiated from the notch in a substantially omnidirectional radiation pattern. If desired, the notch may have approximately the same radiation characteristics as a standard handset monopole without the disadvantage of being an external attachment. Accordingly, antennas according to embodiments of the present invention may eliminate the need for an additional antenna component.
Notch antennas may be provided with various configurations according to additional embodiments of the present invention. For example, antennas according to the present invention may be particularly well suited for use as GPS antennas. Furthermore, because of their compact size, antennas according to the present invention may be easily incorporated within small communications devices. The exemplary notch antenna structure described above could also be implemented in a variety of orientations in a wireless communicator to provide multiple different antenna functions. Moreover, more than one of the above described notch antennas could be implemented simultaneously in a singular wireless communicator to function, for example, as a primary communications antenna and a GPS antenna.
According to another embodiment of the present invention, a wireless communicator is provided that implements the notch antenna described above as a primary communications antenna. The wireless communicator preferably includes a housing, a PCB disposed within the housing, a notch antenna formed within a ground plane within the PCB, and an RF signal feed that electrically connects the notch antenna to RF circuitry on the PCB. The PCB has a surface and an elongated configuration that defines a first direction. The notch is preferably formed in the ground plane along a second direction that is transverse to the first direction.
When a wireless communicator incorporating a notch antenna according to this embodiment of the present invention is oriented such that the first direction is vertical, the notch is configured such that predominantly vertically polarized electromagnetic waves are radiated from the notch in a substantially omnidirectional radiation pattern in response to RF signals. Notch orientation may be important since it may, in part, determine the polarization characteristics of a wireless communicator. For instance, a horizontal orientation of a notch may facilitate vertical polarization, which is highly desirable in, for example, radiotelephones since vertically polarized waves are most easily radiated from a vertically elongated handset. Integrating a notch antenna into a printed circuit board (PCB) may eliminate the need for an additional antenna component.
The opposite side portions of a notch antenna according to the present invention can have a variety of configurations. For example, a notch may be configured to have opposite side portions that (1) are substantially parallel, (2) have a meandering configuration, (3) have a mirror image configuration, or (4) a flared apart configuration. The portion of a PCB underlying a notch is preferably void of conductors associated with other circuit functions on all layers of the PCB. In addition, it is preferable that shield cans not cover a notch of the present invention.
A closed end of the notch may have a width greater than the width of the open end of the notch. The length of a notch antenna preferably does not exceed a quarter wavelength of the lowest frequency of operation. The RF signal feed is electrically connected to each of the notch side portions and to the RF circuitry that receives or transmits RF signals. The RF signal feed can be any unbalanced line that is connected to one side portion of the notch and that extends across the notch to the ground plane conductor on the opposite side portion of the notch.
The position of a notch in a PCB may be important. A notch may be located in a portion of a PCB that is disposed in the upper end portion of the housing, and in a preferred embodiment, the notch is positioned at least 20 mm from the upper end portion of a housing. To maximize bandwidth, a notch may be located in the middle or center of a housing. However, a notch may be preferably located in a position that will not be covered by a user""s hand during operation of a device incorporating a notch antenna according to the present invention. Wireless communicators according to other embodiments of the present invention may include at least one impedance matching circuit. Resonance can be achieved artificially by dielectrically loading a PCB or by addition of an impedance matching circuit comprising one or more capacitors. While an impedance matching circuit may be configured in any manner to match impedance of a notch to a desired impedance, an impedance matching circuit may include at least one of a series capacitor that bridges a notch adjacent an open end and a shunt capacitor positioned adjacent a side portion of the notch. Accordingly, a notch antenna according to embodiments of the present invention may be implemented in a wireless communicator as a primary communications antenna.
In other embodiments a notch antenna of the present invention may be implemented as a GPS antenna in a wireless communicator that also includes a primary communications antenna. A notch antenna may be particularly useful when used for GPS reception since the narrow GPS bandwidth may allow the size of the notch to be smaller than the size of a notch when used as a primary antenna. According to this embodiment of the present invention, a GPS notch antenna includes opposite side portions. A GPS signal feed is electrically connected to each of the side portions and to GPS receiver circuitry on the PCB incorporating the notch. According to this embodiment of the wireless communicator, a primary antenna is preferably arranged such that it is polarized orthogonally with respect to the polarization of the GPS notch. In addition, the GPS notch antenna preferably provides a high out-of-band VSWR, which may facilitate good isolation in, for example, cell phone frequency bands. In other words, a GPS notch antenna configured to resonate in a narrow frequency band may help to suppress the coupling to other antennas (i.e., primary communications antennas) outside the GPS band.
According to another embodiment, a GPS notch antenna may be configured such that the notch is polarized in a second polarization direction substantially orthogonal to a first polarization direction. This configuration may be advantageous for a variety of reasons. First, a vertical orientation of the notch makes the polarization nominally orthogonal to that of a primary cell phone antenna. The combination of polarization orthogonality and out-of-band mismatch may provide good isolation across all bands in which coupling could be a problem. To configure the notch specifically for GPS reception, the notch is preferably located in a central portion of a PCB that is disposed adjacent the upper end portion of a housing. As a result, isolation between the primary antenna and the notch may be greater than 20 dB in a frequency band between 500 MHz and 2.5 GHz. Accordingly, a notch antenna according to the present invention may be implemented as a GPS antenna in a wireless communicator which also includes a primary communications antenna.
Other embodiments of the present invention may utilize two or more notch antennas. A first notch may be configured to resonate as an RF antenna within a selected frequency band. A second notch may be configured to resonate within a selected frequency band as a GPS antenna. Accordingly, wireless communicators according to this embodiment of the present invention may implement multiple notch antennas each serving different purposes and performing different functions.
According to another embodiment of the present invention, a surface mount notch antenna is provided. The surface mount notch antenna includes a dielectric substrate, a conductive layer, a notch, and a conductive pattern. The dielectric substrate preferably has opposite first and second surfaces, and opposite edge portions. A conductive layer is disposed on the first surface and a notch is formed in the conductive layer. The notch preferably has opposite sides and an open end. The notch is configured to resonate as an antenna within a selected frequency band. The conductive pattern preferably has a first portion disposed on the second surface, a second portion, and a third portion disposed on the first surface. The first, second, and third portions may be electrically connected. The conductive pattern preferably serves as a feed pad for connecting the surface mount antenna to a feed line. The third portion can be electrically isolated from the conductive layer disposed on the first surface. The conductive pattern is preferably configured to adjust the impedance of the notch. The dielectric substrate may also include at least one ground pad contacting the conductive layer. This ground pad is used for grounding the conductive layer of the surface mount antenna when the antenna is mounted within a wireless communicator.
Depending on the configuration of the notch and the dielectric constant of the dielectric substrate, the notch may or may not resonate naturally. In the case of natural resonance, the impedance of the notch varies monotonically along the length of the notch (i.e., from a relatively high impedance near the open end of the notch to zero at the shorted end). The 50 xcexa9 point may be determined, and the notch may be fed directly without additional components.
If the notch is non-resonant, it may be necessary to provide some additional matching. This may be provided, for instance, by utilizing a capacitive network integrated into the structure of the surface mount component. For example, the conductive pattern, in conjunction with the conductive layer, may preferably comprise at least one capacitor, while the first portion serves as at least one plate of the at least one capacitor. Optionally, the first portion serves as at least one series capacitor plate and at least one shunt capacitor plate. This may provide the required impedance matching.
The second portion may have a variety of configurations. For instance, the second portion may be a conductive via passing through the dielectric substrate, and the first and third portions can be electrically connected by the conductive via. Alternatively, the second portion may be a conductor disposed along an edge portion of the dielectric substrate.
An antenna component according to the present invention may be implemented in a wireless communicator including a housing, a printed circuit board (PCB), a first notch and a plurality of contacts. The PCB includes a ground plane, and has the receiver or transmitter circuitry thereon. The first notch is formed in the ground plane, and includes first opposite side portions and an open end. The surface mount antenna component includes at least one and preferably a plurality of ground pads and at least one signal pad. The ground pads are preferably located on the first dielectric substrate and come in contact with a plurality of contacts connected to the ground plane, and positioned around a periphery of the first notch. These ground pads allow the surface mount antenna component to be grounded thereto. The signal feed pad contacts a feed line to connect the surface mount antenna component to the wireless communicator. A first notch is formed in the ground plane; however, the first notch does not function as the antenna. Instead, the first notch is slightly larger than the second notch. The contacts are preferably located along the opposite side portions of the first notch and facilitate connection to a surface mount antenna component.
According to another embodiment of the present invention, a surface mount antenna is provided that includes a first dielectric substrate, a first conductive layer, a notch, a conductive pattern, a second dielectric substrate and a second conductive layer. The first dielectric substrate has opposite first and second surfaces and opposite edge portions. The first conductive layer is disposed on the first surface. The notch is preferably formed in the first conductive layer, and has opposite sides and an open end. The notch is configured to resonate as an antenna within a selected frequency band.
The conductive pattern has a first portion disposed on the second surface, a second portion, and a third portion disposed on the first surface. The first, second, and third portions are electrically connected, and the third portion is electrically isolated from the conductive layer disposed on the first surface. The second dielectric substrate has opposite third and fourth surfaces. The third surface is disposed in a contacting relationship with the conductive pattern. The second conductive layer is disposed on the fourth surface to capacitively couple the second conductive layer to the first conductive layer. The first dielectric substrate may also include at least one ground pad contacting the first conductive layer. The ground pad is used for grounding the first conductive layer of the surface mount antenna when the antenna is connected to a PCB within a wireless communicator.
The conductive pattern may serve as a feed pad for connecting the surface mount antenna to a feed line. The first and third portions are electrically connected by the second portion. For example, the second portion may be a conductive via passing through the first dielectric substrate. The second portion may be a conductor disposed on an edge portion.
According to additional embodiments of the present invention, notch antenna components may also be provided with multiple dielectric substrate layers to achieve the required values of capacitance. As such antenna components according to the present invention may be useful in a wide variety of wireless communication devices. In addition, various conductor dimensions of these surface mount antenna components may be precisely trimmed with a laser etcher thereby allowing precise control of the frequency of resonance. This may reduce the bandwidth previously required to allow for component tolerances. By reducing the bandwidth required, notch antennas according to the present invention can be small in size.